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Broken clutch lifter plate... What next?
cbxman:
Just an update on the broken clutch.
I should have said "Broken Pressure Plate", not "Lifter Plate". Silly me.
I sourced a partial clutch basket, which had an intact pressure plate. The basket and hub was from a pre K6 bike but fitted on to a K6 'Driven Sprocket'. It was bit chewed up at the back where the circlip portion of the shaft had ground its way into the back of the basket. Still it is OK so I have spare basket, and hub which will fit the K1.
After many hours of searching about broken 'lifter plates' and 'pressure plates' It seems that there is no defined procedure to follow. There were two well defined issues with installing these 750 clutches...
1 Misaligning the hub with the pressure plate. The pressure plate can only be fitted to the hub in only 2 of the four possible positions. The splines must fit into the splines of the pressure plate, or you will break the pressure plate. This is what had happened to my bike by some PO.
2. The 'Lifter Plate' is a favourite for breaking. It is said that the uneven tightening of the four fasteners through springs will cause it to break. The spring posts slot into the reverse side of the lifter plate towards the end of tightening down. If the sequence is uneven, the plate can tilt and then hang up on the edge of one of the spring post. Further tightening will crack the lifter plate.
However, I have found another failure mode, which I have not seen posted anywhere, so I thought I would mention it here.
3. I was tightening the post fasteners and one became harder to turn than the other three. Using a small angled mirror and a torch, I could see under the lifter plate and saw that the end of one of the clutch springs had dropped into the groove on the reverse of the lifter plate where the post should go in. Had I carried on tightening that fastener, it would have snapped the lifter plate.
So these clutches are really tricky to install.
Having said all that, I'm happy to say that after a test ride this afternoon the clutch was working well....I could actually move to neutral from 1st whilst stationary!! Changing up and down the box was excellent.
I hope that helps someone who is considering working on their clutch.
Cheers,
Jerry
Lobo:
Not quite the answer we’d all like, but rebuilding the clutch with the engine in the (clutch) vertical plane solves the issues.
Have just had my ‘750 engine rebuilt on a very nice jig that rotated the engine anyway-up, with Lindsay (rebuilder) commenting on how easy it is to damage clutches if doing so in the normal orientation.
A fair amount of jiggling, tightening, jiggling still involved…
cbxman:
Lobo,
I agree. if the clutch is lying on its back, then the springs will naturally keep straight. I expect that most people will be servicing the clutch with the engine still in the bike though. With gravity trying spoil your day!
Cheers,
Jerry
Lobo:
As an aside, Lindsay (Donai) is a fairly well known (Period 2) sidecar racer here in Oz, and primarily raced Honda 750 rigs some 40+ years. He builds / modifies all his own bikes / engines etc, inc engineering some extremely fancy exhaust systems. ANYWAYS, whilst rebuilding my clutch he pointed to a shelf of nothing but CB750 clutches, and commented that a ‘750 clutch assy will typically last one day on the track. Bloody hell.
And of course, they’ll be changed in the ‘normal’ position, so I guess the engine on its side in my case was here nor there to him!
cbxman:
Lobo,
Being aware of these pitfalls means you can relax when re-installing them.
I was being ultra cautious as these parts are getting really hard to get.
I could so easily have broken that lifter plate if I had not stopped and checked.
Cheers,
Jerry
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